I just barely tried it as I have to learn some songs tonight, so not much time to fart around. The last amp sim I messed with was the Marsh BE. Without anything to compare it to, since I don't use the amp sims on a regular basis, seemed nice and responsive. When I switched to the JCM 800, which was the amp sim I had intended on using and passed on since it wasn't cutting it at the time, seemed a lot better than I remembered. I'm looking forward to spending some time with it this weekend and really seeing what it can do. I actually have an 800 that I lent out with the intention of selling it. I'll get it back and do some serious comparisons.
I fully admit that I am the wrong person to judge, as I am not just looking for "a good sound" by rather "my" sound. Harder to achieve when your amp isn't in there. First impressions though, I'm very optimistic. It did "feel" better, I have to admit. Kudos Cliff.